PROJECT SUMMARY/ABSTRACT Circadian rhythms are 24-hour oscillations in behavior and physiology that are conserved in almost all forms of life on earth, enabling organisms to adapt to earth?s diurnal cycles. Dysregulation of circadian clocks has been linked to many human pathologies, including diabetes, obesity and neurodegenerative diseases. The long-term goal of my research is to understand how circadian clocks are regulated and how their disruption leads to human pathologies. In the next five years, I propose to investigate the neural and molecular basis of circadian regulation in response to two external cues: temperature and food. Circadian rhythms are self-sustained in constant conditions, but they have to be entrained/adjusted by external cues such as light, temperature or food cycles daily to maintain a precise 24-hour period. Past pioneering work has uncovered the major clock components and the mechanisms underlying light entrainment and sleep-wake rhythms. However, the neural and molecular mechanisms by which other external cues, temperature and rhythmic food intake, entrain the clock and the related input and output mechanisms remain largely unexplored. I recently achieved a breakthrough in understanding how circadian clock neurons process temperature information to regulate sleep-wake rhythms. In this proposal, I seek to investigate the neural and molecular mechanisms underlying temperature entrainment and food entrainment in Drosophila melanogaster, a powerful model organism as it has a highly conserved clock similar to humans along with superb genetic and behavioral tools. Specifically, I will first elucidate new temperature input pathways and reveal the neural and molecular mechanisms that govern sleep-wake rhythms under temperature cycles. In these efforts, I will use a multidisciplinary approach combining novel instrumentation along with powerful genetic, molecular, behavioral, and live imaging approaches. Next, to elucidate the mechanisms underlying food entrainment, I will leverage novel high-resolution calorimetry and other tools that I recently developed that makes it possible, for the first time, to both control the timing of food intake and monitor metabolic rhythms from individual organisms. This work will uncover fundamental and important new insights into circadian regulation which are expected to be highly evolutionarily conserved. Further, this work can have several practical benefits as it may provide new opportunities for the development of novel strategies to target clock machinery to treat diseases.